Limited knowledge regarding the pathophysiology of intrauterine growth restriction (IUGR) emphasizes the need for studies which explore the mechanism(s) responsible for regulating fetal growth under both normal and compromised conditions. Studies were performed with the fetal monkey with the goal of characterizing normative baseline values for the insulin-like growth factors (IGF-I, IGF-II), which are key effectors of fetal growth and are modulated by serum carrier proteins (IGF binding proteins [IGFBPS]). IGF-I, IGF-II, and IGFBP-3 were studied in the rhesus (macaca mulatta) and long-tailed (macaca fascicularis) monkey fetus and dam during the second and third trimesters of pregnancy. Serial fetal blood samples were collected by cardiocentesis every 10 days from gestational day (gd) 90 - 160, and at 1 month postnatal age; maternal blood samples were collected at similar timepoints. Results indicated that maternal sera IGF-I and IGF-II did not change significantly whereas fetal concentrations of serum IGF-I and IGF-II increased approximately two-fold during the second to third trimesters. No significant differences were detected between the two species. Western-ligand blot analysis revealed predominant IGFBPS of 45-40 (IGFBP-3) and 28 KDA (IGF BP-1) in both maternal and fetal compartments, and western-immunoblot analysis using a specific antisera against IGFBP-3 indicated 45-40 and 28 KDA immunoreactive forms. Although IGF-I, IGF-II, and IGFBP-3 remained relatively unaffected in maternal sera during this period of gestation, fetal concentrations of IGF-Ii, IGF-II, and IGFBP-3 increased in a developmental profile similar to the human fetus. Future investigations with the fetal monkey will provide essential information on the role of the IGF axis in fetal growth in health and disease, which will be directly applicable to the human fetus under normal and growth-compromised conditions.